The present invention relates to a process for improving hiding efficiency in pigmented paints. Latex binders that adsorb to TiO2 are known to form composites with TiO2, leading to greater pigment efficiency in paint films. It is possible to use the adsorbing polymer as a portion of the binder in the paint (pre-composite) to maximize hiding and to use a second non adsorbing (let-down) binder to achieve other desired properties and to reduce cost. One of the problems often observed with current pre-composite technology, particularly pre-composites prepared using highly reactive functional monomers such as phosphoethylmethacrylate (PEM), is formation of grit occurring during the preparation of the composite and arising from the uncontrolled reaction of the reactive pre-composite with TiO2. To control grit, the formulator must carefully mix the adsorptive latex with the pigment under controlled conditions to avoid flocculation, which often requires expensive high shear mixing.
Alternatively, grit can be controlled using less reactive pre-composites, for example, pre-composites prepared from less reactive monomers such as itaconic acid; unfortunately, coatings formulations made from these pre-composites exhibit significantly less hiding than coatings made from the more reactive pre-composites. Therefore, it would be an advantage to reduce grit formation and improve hiding in formulations that include latex binder and TiO2, in a controlled and cost-effective manner.